Many industrial structures include joints joining beams or plates. Often, these joints are load carrying and their integrity is critical to the strength of the entire structure.
While visible inspection is sometimes easy when the beam or plate is exposed, it is often hard or impossible to view the entire joint structure. For example, screws binding a beam may become partially loose or develop cracks, compromising the joint structural integrity without having any visible signs.
Often, the catastrophic breakdown of a structure starts with a failure of a weak or damaged joint. Often, integrity of a joint deteriorates due to fatigue, corrosion or mishandling such as incorrect assembly after maintenance action.
Methods for monitoring structural integrity have been developed, however there is a need for system and method for monitoring strength and integrity of a joint without the need to disassemble said joint.
Condition-based maintenance of structural components assisted by a real-time monitoring is a relatively new arena enabling cost effective maintenance and improved functional reliability of the structure. Emergence of this field has been enabled by intensive developments of Structural Health Monitoring (SHM) systems during the last few decades.
Several recent reviews discuss methods employed in detection, allocation, and evaluation of various types of structural damage [1-6]. Basically, SHM systems consist of a physical device for data collection and a signal-processing computer along, with an appropriate algorithm. Efficient identification of the onset of damage, or deterioration, at the earliest possible stage; centers on the sensitivity of a selected diagnostic parameter of structural response to the type of damage to be detected. That sensitivity is reflected in the design of the monitoring device and in the selected signal-processing algorithm.
Currently, SHM systems rely mainly on three diagnostic parameters considered as structural markers: modal properties of vibrating structures, propagation of Lamb waves, and impedance of the structure as sensed by attached PZT wafers.
Recently, Pandurangan and Buckner [7] suggested the use of modal damping ratios as another marker for monitoring single-lap adhesive joints. Their experiments reveal that the sensitivity of this method is favorable in comparison with frequency-based methods.
It should be noted that sometimes a small defect which causes a minor effect on the total strength of a joint, for example, a small crack at the joint, may develop rapidly under deteriorating conditions, causing catastrophic failure of the joint. Thus, it is important to detect, identify and correct a defect be tore its rapid progression.